In known dispensing devices, the annular space around the outside of the cover endpiece is empty of material for the sake of economy, and until now, covers have been put into place by means of machines that are required to maintain very accurate alignment of the endpiece and the control rod prior to the cover being snapped into place in order to avoid any risk of fixing the cover with the control rod not being engaged in the endpiece, but extending obliquely outside the endpiece in the above-mentioned annular space, it being of great importance to avoid such a situation since it can lead to the control rod being broken or to the receptacle being emptied.
European patent application No. 0 037 903 discloses a device for dispensing a substance stored under pressure in a receptacle, and including a cover for snapping onto the receptacle. The receptacle has a control rod valve which is opened by applying axial thrust to the control rod. The control rod is fixed on the body of the receptacle by means of a cup. The device includes an endpiece for engaging on the control rod and co-operating therewith to form a channel for delivering the substance. The bottom of this endpiece has a cylindrical portion that slides on a projection formed in the center of the cup. The endpiece can be lowered onto the control rod only if the bottom cylindrical portion of the endpiece has previously been engaged on the projection of the cup. Not only does such a device require a special shape of cup carrying the control rod, it is also applicable solely to a receptacle provided with a control rod which opens when subjected to axial thrust.